Shiitake mushrooms should be cooked in water for about 2-3 minutes. To blanch with hot water, blanch for 2 minutes. When using cold water, blanching for 3 minutes is best. This time ensures that the mushrooms are cooked and remain firm. Blanching for too long will cause the mushrooms to lose their toughness and the flavor will deteriorate. Too short a blanching time will result in mushrooms that are not crisp and smooth.